The present invention relates to improved methods for transferring a layer of material from a source substrate onto a support substrate during the fabrication of composite substrates, in particular for optics, optoelectronics, or electronics.
Novel techniques have recently been developed for transferring a layer of a material, such as a processed layer of semiconductor material, from a first or “source” substrate onto a second or “support” substrate. The term “processed layer” means a layer of material that has undergone some or all of the steps of a technique for forming electronic components. Transfer techniques may use a source substrate that has a weakened zone that was formed by implanting atomic species, or a substrate having a buried porous zone, or a substrate with two layers that have been bonded to each other at a bonding interface by using a controlled bonding energy. Such techniques are described briefly below with reference to FIGS. 1 to 3.
In FIG. 1, the source substrate 1 includes a weakened zone formed by using one of the techniques mentioned above. The source substrate is brought into contact with a support substrate 2 to form a stack. The layer to be transferred 11 is then detached from the remainder 12 of the source substrate along a zone of weakness 13 of the substrate. The layer 11 may be detached by introducing mechanical stresses, such as tension and/or bending and/or shear stresses. The mechanical stresses can be applied, for example, by a pulling rig, by a cutting blade applied to the side of the stack at the zone of weakness 13, or by a jet of fluid or liquid, or gas applied laterally to the zone of weakness. The mechanical stresses encourage the propagation of a crack along the zone of weakness 13.
The two substrates 1 and 2 could be connected to each other by molecular bonding, without using an adhesive or an adhesive film. Transfer of the layer 11 is possible if the mechanical retention of layer 11 of the source substrate 1 is well below the mechanical retention of the layer 11 of the support substrate 2. However, that condition may no longer be satisfied if adhesive is used since the exact volume of deposited adhesive is difficult to control. As can be seen in FIG. 2, the adhesive 3 very often projects outwardly 30 beyond the respective side faces 10, 20 (or sides) of substrates 1, 2 to cover or mask the periphery of the zone of weakness 13. It is very difficult to properly detach the layer 11 from the substrate 1 by applying mechanical stresses when the periphery of the zone of weakness 13 is covered. In particular, the mechanical force required to detach the layer 11 is very high, and as shown in FIG. 3, could result in a fracture of the substrates and in particular of the support substrate 2 along fracture lines 21. The fracture lines may not extend in the plane of the zone of weakness 13, but can occur in a random and unpredictable manner throughout the thickness of the substrate 2.
It would be beneficial to provide a technique that overcomes the disadvantages described above to improve mechanical transfer methods. In addition, it would be advantageous to provide a method that prevents excess material at a bonding interface from covering the peripheral edge of the zone of weakness. The present invention now provides such methods.